Heroin abuse is a growing problem in the United States today. Because of this, an understanding of the mechanisms by which heroin exerts its reinforcing effects on the brain will contribute important information to the development of potential treatments. It is possible to study brain mechanisms in the awake animal by recording from chronically implanted electrodes during drug self-administration behavior. This technique allows one to record from many neurons at once; additionally, the use of awake, behaving animals allows one to examine the cue processing and task sequencing associated with drug self-administration. Heroin is a drug of abuse which has not been examined to a great extent with this technique. Therefore, the long-term objective of this proposal is to determine whether the neural firing patterns associated with heroin may be similar to those correlated with other reinforcers (such as food), and therefore whether there may be generalized patterns of reinforcement- related neural activity which might drive the acquisition or consumption of reinforcing substances. This would also support the hypothesis that there may be common reward mechanisms for both natural reinforcers and drugs of abuse. Specifically, this proposal will 1) characterize the patterns of neural firing within the mesolimbic dopamine system during heroin self-administration; 2) compare these firing patterns with those elicited by natural reinforcers, such as food; 3) examine the involvement of opioids and dopamine in generating the observed neural firing patterns. Neural activity will be recorded from the nucleus accumbens, prefrontal cortex, and ventral tegmental area of rats performing a multiple operant schedule task maintained by food and heroin. Neural data will be analyzed by looking at firing rates and patterns correlated with several temporal nodes along the task continuum. Insight into the mechanisms by which various reinforcers act may shed light on the process of reward in general.